About 70% of human birth defects, which range from 3% to 6% of all births in the United States, are thought to result from maternal and, thus, conceptus exposure to chemicals currently marketed, of which 38,000 exist. Less than 10% of the chemicals marketed (2,800) have been tested for teratogenic activity with standard rodent and rabbit developmental tests. Risk evaluation of untested agents is essential to assure health safety for unborn humans, yet assessing teratogenicity with standard whole animal tests is unlikely given the expense, animal use, and study duration for testing a single agent ($50,000 to $100,000, 80 pregnant rodents and 48 pregnant rabbits, three to five months for testing and reporting). Although standard tests are fundamental for definitive assessment of risk to the unborn human, they are best used for hazard assessment of agents with suspected developmental activity rather than for screening agents of unknown activity. To alleviate burden of the initial teratogenic assessment now carried by the standard tests, developmental toxicity screens, which employ test subjects other than the intact pregnant mammal, have been designed. The role of the screen is to simply, inexpensively, and with confidence detect developmental hazards and, thereby, leave the standard tests free for the ultimate decision on an agent's potential toxicity to unborn humans. This proposal addresses further development and verification of the brine shrimp assay, a nonmammalian teratogenic screen which employs developing Artemia nauplii, to evaluate biological fate and effect of chemicals administered to pregnant mammals. The main objective is to expand the capacity of the assay by validating its ability to screen test chemicals for developmental toxicity in mammals. The shrimp will be exposed to the same parent chemicals and metabolites that are experienced by the mammalian conceptus in vivo; the response of the shrimp will therefore indicate possible outcomes from exposure of the mammalian conceptus. The specific aims are: (1) to develop shrimp culture media using body fluids collected from pregnant test animals and concepti for evaluating fate of chemicals; (2) to measure biosynthetic activities (macromolecular synthesis, gene expression) in the shrimp that are common across species and correlate these activities with phenotypic changes occurring in the shrimp; and (3) to validate the assay by testing its ability to determine the activity of known mammalian teratogenic agents, either mixed directly with saline culture medium and body fluids or present in body fluids collected from treated rats.